The retailer, based in Issaquah, Washington, held $3.47 billion of net cash as of September, the most in at least two decades, even after spending about $760 million to acquire the partner in its Mexican joint venture.

Galanti said on an analyst call last month that there wasn’t “a great sense of pressure to change our modus operandi” with regard to dividends.

“It’s a tangible way of rewarding shareholders that avoids the lottery of a share buyback,” said Bryan Roberts, an analyst at Kantar Retail in London. “They’ve amassed significant cash reserves, partly due to their success. They have been one of the most successful retailers in the past 20 years.”

Costco said comparable sales rose 6 percent in the four weeks ended Nov. 25, with growth slowing from 7 percent in the previous month. Excluding the effects of gasoline prices and currency movements, monthly growth was 5 percent, it said, unchanged from October.

The special dividend will be paid on Dec. 18 and is in addition to the regular quarterly cash dividend of 27.5 cents a share that was declared on Oct. 30, Costco said.